Method for preparation of polycarboxylate superplasticizer by graft copolymerization of fatty acid vinyl ester onto acrylate polymer

A preparation method of a polycarboxylate superplasticizer by graft copolymerization of fatty acid vinyl ester onto acrylate polymer, comprising a polymerization step, a graft copolymerization step, an alcoholysis step and a hydrolysis step in sequence, wherein:

• (1) polymerization:
• firstly the organic solvent was added to the reactor with a risen temperature to 60-130° C. followed by adding molecular weight regulator, and then the mixture of acrylate and initiator was dropped for 1-10 hours. After reaction for 0.5-5 hours at the constant temperature, the organic solvent was removed by vacuum distillation, and then the polymerization product namely polyacrylate was obtained;
• (2) graft copolymerization:
• the above polymerization product, water, emulsifier and molecular weight regulator were orderly added to the reactor with a risen temperature to 50-95° C. for stirring 10-30 minutes until homogeneously mixed. Then the fatty acid vinyl ester and initiator aqueous solution with a mass fraction of 5-50% were added respectively for 1-10 hours. After reaction for 1-5 hours at the constant temperature, the temperature was lowered to 25-40° C. and the obtained emulsion mixture was demulsified by adding inorganic salt saturated solution followed by 2-5 times of washing with deionized water, and then the graft copolymerization product was obtained;
• (3) alcoholysis:
• the above graft copolymerization product was mixed with alcohol solvent and then added to the reactor with a risen temperature to 30-70° C. followed by adding inorganic base. After alcoholysis for 10-120 minutes, the alcohol solvent and by-products were removed by vacuum distillation, and then the polyacrylate-g-polyvinyl alcohol was obtained after drying;
• (4) hydrolysis:
• the above polyacrylate-g-polyvinyl alcohol was mixed with water and then added to the reactor with a risen temperature to 30-70° C. followed by adding inorganic base. After hydrolysis for 10-120 minutes, the water solvent and by-products were removed by vacuum distillation, and then the polycarboxylate superplasticizer solution with a required concentration was finally obtained by adding an appropriate amount of water;
• wherein in step (1), the organic solvent used in polymerization was methanol, ethanol, p-xylene, 200# solvent oil, glycol, toluene or cyclohexane, with the mass ratio of 2-10:1 to the acrylate;
• the molecular weight regulator used in polymerization was isopropanol, 1-dodecanethiol or isooctyl 3-mercaptopropionate, with the molar ratio of 0.001-0.05:1 to the acrylate;
• the acrylate used in polymerization was methyl acrylate, ethyl acrylate, n-propyl acrylate, butyl acrylate or amyl acrylate;
• the initiator used in polymerization was azobisisobutyronitrile, 2,2′-azobisisoheptonitrile, benzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate or di-tert-butyl peroxide, with the molar ratio of 0.001-0.05:1 to the acrylate;
• in step (2), the mass ratio of added water to polyacrylate mentioned in step (1) was 5-50:1;
• the emulsifier used in graft copolymerization was sodium laurate, sodium dodecyl sulfonate, sodium dodecyl sulfate or sodium stearate, with the molar ratio of 0.00002-0.004:1 to the added water;
• the molecular weight regulator used in graft copolymerization was 1-dodecanethiol, isopropanol, mercaptoacetic acid or mercaptopropionic acid, with the molar ratio of 0.001-0.05:1 to the fatty acid vinyl ester;
• the fatty acid vinyl ester used in graft copolymerization was vinyl acetate, vinyl propionate or vinyl butyrate, with the molar ratio of 3-45:1 to the acrylate mentioned in step (1);
• the solute of initiator aqueous solution used in graft copolymerization was potassium persulfate, sodium persulfate or ammonium persulfate, with the molar ratio of 0.1-0.2:1 to the acrylate mentioned in step (1);
• the inorganic salt saturated solution used in graft copolymerization was saturated sodium chloride solution, saturated calcium chloride solution or saturated aluminum chloride solution;
• in step (3), the alcohol used in alcoholysis was methanol, ethanol or propanol, with the molar ratio of 2-5:1 to the fatty acid vinyl ester mentioned in step (2);
• the inorganic base used in alcoholysis was sodium hydroxide or potassium hydroxide, with the molar ratio of 0.001-0.01:1 to the alcohol;
• in step (4), the molar ratio of water used in hydrolysis to the acrylate mentioned in step (1) was 2-10:1;
• the inorganic base used in hydrolysis was sodium hydroxide or potassium hydroxide, with the molar ratio of 0.001-0.01:1 to the water used in hydrolysis.